Download 25 - Transport in Plants.notebook

25 ­ Transport in Plants.notebook
February 21, 2013
Chapter 25 ­ Transport in Plants
Flowering plants are made up of roots, stems, leaves and flowers.
Roots
The roots grow down towards gravity (Geotropism)
They anchor the plant to give support
They take in water and minerals
They can store food, e.g. Carrots
Stem
The stem supports the leaves and flowers.
It carries water and minerals from the roots
to the shoots.
It carries food from the leaves all around the plant. R. Cummins
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25 ­ Transport in Plants.notebook
February 21, 2013
Water transport in Plants
Xylem ­ carries water and dissolved minerals from root to leaf.
Xylem is made of cells like straws (vessels) that can let water move up through them. The water moves in a stream from the roots, up through the plant into the leaves and out of tiny pores under the leaves called 'stomata'.
This movement of water is called the ' transpiration stream'. Transpiration ­ is the loss of water vapour from the surface of a plant.
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25 ­ Transport in Plants.notebook
February 21, 2013
Mineral uptake by diffusion
Plants use active transport (needs energy) to take in minerals from the soil.
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25 ­ Transport in Plants.notebook
February 21, 2013
Root Pressure
Water is drawn into the root hairs and root cells by Osmosis.
Water keeps moving into the cells and moves from cell to cell.
The cells become full and turgid and the water moves up the plant.
Osmosis 'pushes' the water up to the height of about 1 metre.
This is called root pressure.
Root pressure is not strong enough
to get water up to the top of tall trees.
For this the plants use evaporation.
The evaporation pulls the water out of
the plant and pulls up the next drop of
water to be evaporated.
This is called the Cohesion­tension model of water transport.
A cut stem shows root pressure.
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25 ­ Transport in Plants.notebook
R. Cummins
February 21, 2013
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25 ­ Transport in Plants.notebook
February 21, 2013
Control of Transpiration by the Leaves
1. The waxy cuticle on the leaf surface stops water loss.
2. Stomata are underneath the leaf to reduce evaporation.
3. Guard cells open during the day and close at night.
They can also close by the day when,
> the plant looses to much water, > the temperature is too high (too much evaporation)
> the wind is too strong (too much evaporation).
Carbon Dioxide is the main controller the of stomata.
The guard cells fill with water and become turgid.
This keeps the stomata open.
If the guard cells have little water then they collapse.
This closes the stomata to prevent more water loss.
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25 ­ Transport in Plants.notebook
February 21, 2013
Transverse section of a leaf
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25 ­ Transport in Plants.notebook
February 21, 2013
Carbon Dioxide and Glucose
Photosynthesis takes place in the mesophyll (ground tissue) in the leaf.
Sources
Most carbon comes from CO2 in the air. It diffuses into the leaf by the stomata.
We can measure this uptake and it's called the apparent rate of photosynthesis.
The other source of CO2 is from respiration. The gas is recycled in photosynthesis. The real rate of photosynthesis is got by adding the amount taken in from the atmosphere (apparent rate) to the amount produced by respiration. Products of photosynthesis
The Oxygen produced by the leaves is either released by diffusion
or is recycled in Respiration.
The Glucose produced is used in respiration or stored as starch in the
spongy mesophyll.
The Glucose can also be moved by diffusion into the phloem sieve cells.
From here it can be transported around the plant for energy or storage.
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25 ­ Transport in Plants.notebook
February 21, 2013
Modified Plant Food Storage Organs
Modified organs are organs that have been
changed in order to store more food for the plant. Carrot Tap­roots
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Modified leaves in onions
Modified stems in potato
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